Make reductionScale smoother
Making the second part of the formula smoother, changing it to a linear
function, increasing steadily as reductionScale increases and at the
same time, it should be a little bit simpler, therefore the
simplification bounds.
Passed STC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 83040 W: 21493 L: 21322 D: 40225
Ptnml(0-2): 252, 9848, 21209, 9899, 312
https://tests.stockfishchess.org/tests/view/6762145486d5ee47d9543242
Passed LTC:
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 230124 W: 58485 L: 58478 D: 113161
Ptnml(0-2): 175, 25620, 63484, 25589, 194
https://tests.stockfishchess.org/tests/view/6762d4ef86d5ee47d9543367
closes https://github.com/official-stockfish/Stockfish/pull/5725
Bench: 1204658